Study of P21 Expression in Oral Lichen Planus and Oral Squamous Cell Carcinoma by Immunohistochemical Technique.

STATEMENT OF THE PROBLEM
Lichen planus is a mucocutaneous disease that is relatively common in middle aged individuals. Some studies have shown that oral lichen planus has a potential to progress to squamous cell carcinoma.p21 is a cyclin-dependent kinase inhibitor that regulates the cell cycle, thus it acts as an inhibitor in cell proliferation.


PURPOSE
This study was aimed to evaluate and compare the immunostaining of p21 (as a proliferation inhibitory factor) in oral lichen planus (OLP) and oral squamous cell carcinoma (OSCC).


MATERIALS AND METHOD
In this descriptive cross-sectional study, p21expression was investigated in 24 samples of oral lichen planus (OLP), 24 samples of oral squamous cell carcinoma (OSCC) and 24 samples of oral epithelial hyperplasia (OEH) by employing immunohistochemical staining.


RESULTS
The mean percentage of p21-positive cells in OSCC (54.5±6.6) was significantly higher than that in OLP (32.8±6.08) and OEH (9.4±3.8). Moreover, OLP samples expressed p21 significantly higher than the OEH. Kruskal Wallis test revealed a statistically significant difference between the groups regarding the intensity of staining (p< 0.001).


CONCLUSION
According to the findings of this study, the expression of p21 might be related to the potential carcinogenic transformation of lichen planus to SCC. Therefore, continuous follow-up periods for OLP are recommended for diagnosis of the malignant transformations in early stages.


Introduction
Initially described by Erasmus Wilson in 1896, lichen planus is a relatively common chronic skin disease and one of the most common oral mucosal diseases. [1] It is an autoimmune skin and mucosal disorder mediated by T-lymphocytes. [2] Some studies have shown that oral lichen planus (OLP) has the potential to develop to oral squamous cell carcinoma (OSCC). [3][4][5] However, the relation between OLP and OSCC is even now controversial since many researchers believe that still there is not enough data to prove the correlation between OLP and occurrence of cancer. [6] OSCC comprises approximately 90% of oral cancers and is the eleventh most common cancer of human, showing an increased inci-dence. Despite the current improvements in the treatment of this disease, OSCC still has a high mortality rate and its 5-year survival rate is 45-50%. OSCC has different etiological factors; nonetheless, no single causative factor is clearly defined or accepted. [1,[3][4]6] A cancer occurs when mutation or amplification causes dysregulation of the genes that control the cell cycle. [7] The main targets of genetic damage that leads to cancer are four groups of the normal cell cycle regulatory genes; including 1-proto-oncogenes, which accelerate the growth, 2-tumor suppressor or growth inhibitor genes, 3-genes that regulate the apoptosis, and 4genes that are involved in DNA repair. [7] Abnormalities in oncogenes and tumor suppressor genes have been detected in oral carcinoma. [1] Different stages of cell cycle are controlled and conducted by cyclins, cyclindependent kinases (CDK), and their inhibitors. [7][8] p21 protein is a potent CDK inhibitor belonging to the tumor suppressor genes. It binds to CDK and inhibits the RB (retinoblastoma) phosphorylation and the activity of the CDK2 and CDK4 complex which is essential for the cells to enter G1phase. Therefore, it is recognized as a regulator of cell-cycle progression in G1 phase. [7][8] The gene mutations that involve the CDK complex are identified in some malignant neoplasms and are likely to act in favor of cell proliferation process. [7] Only few studies have evaluated and compared the immunostaining of proteins (such as p21) that control the cell cycle in OLP and OSCC. This study was aimed to evaluate and compare the incidence of p21 (as a proliferation inhibitory factor) in OLP and OSCC.

Materials and Method
The samples of this descriptiveanalytic study were collected from the archives of the Department of Pathology, School of Dentistry Isfahan and Hamadan, and Isfahan Alzahra Hospital. A total of 72 samples consisting of 24 paraffin blocks from each of the three lesions; OLP, OSCC, and oral epithelial hyperplasia without dysplasia (OEH) as the control group were recruited.
All the samples were reviewed by a pathologist concerning the criteria described in the related articles. [9-10] Histopathological diagnostic criteria described by Eisenberg, including basal cell hydropic degeneration, band-like lymphocytic infiltrate at epithelial-stromal junction, normal epithelial maturation pattern were considered for diagnosis of oral lichen planus. [10] Cases which were exposed to risk factors such as smoking/drinking behaviors or with dysplastic changes were excluded .Moreover, the patients' medical records should have documented no history of taking medications.
Any sample with improper fixation or with suspicious diagnosis or necrotic tissue was excluded. 15 SCC samples had a moderate to good differentiation and the rest were moderate to poorly differentiated.   The spearman correlation coefficient was calculated to be 0.736 (p< 0.001). In each group, the results are summarized in Table 2. The mean percentages of p21positive cells of SCC (54.5±6.6) ( Figure 1) were considerably higher than OLP (32.8±6.08) ( Figure 2) and OEH (9.4±3.8) (Figure 3).  (Table 3).     [23,[25][26] increased staining of p21 in OLP is likely to show inactivity of its cell-cycle inhibiting role, which in turn might be the initial genetic event in carcinogenesis. [19] The increased staining of p21 in dysplastic lesions that are transforming to carcinomas has been reported by González-Moles et al., [26] although some reports consider this increase in the p21 expression as a response to hyper proliferative condition. [23,26] The results of the current study revealed that among the study groups, the mean age of patients with OSCC was higher than the patients of the other two groups. Also a significant statistical correlation was observed between age and the mean percentages of p21 + cells; this result is in line with the results of the study conducted by Ng et al. [17] They reported a significant relation between p21 expression in OSCC samples and the patients' age; the older the patients were the more likely to express p21. In the present study, no statistically significant relation was detected among p21 expression, the location of the lesions, and the patients' gender; which was consistent with the studies carried out by Ng et al. and Yanamoto et al. [17][18] Regarding the considerable staining of OLP compared to the OEH, and also based on the results of the present and previous studies, oral lichen planus might be considered among the inflammatory diseases that have the potential to progress to carcinoma. [22,24] In future studies, evaluating the association of p21 with other cell-cycle regulators may confirm the results of the current study.

Conclusion
According to the findings of this study, the expression of p21 might be related to the potential carcinogenic transformation of lichen planus to SCC. Follow-up periods are recommended for early diagnosis of the malignant transformations in lichen planus.